Window coverings such as Venetian blinds and cellular shades are typically raised with an outer pull cord. Venetian blinds typically comprise a plurality of horizontal slats suspended beneath a headrail by two or more flexible ladder laces. The ladder laces each include a pair of vertically extending side cords interconnected by a plurality of vertically spaced slat supporting rungs, and the upper ends of the ladders are attached to a ladder drum or tilt drum to tilt the slats in response to turning of the ladder drum. Carriers for the several ladders typically are rotated in unison by a tilt rod. Cellular shades typically comprise a headrail, a bottom rail, and a continuous, collapsible web of material suspended between a headrail and a bottom rail that is raised or lowered with an outer pull cord.
Recent improvements to Venetian blind and cellular shade lifting mechanisms have involved the use of spring motor lifting mechanisms. Spring motor lifting mechanisms provide lifting force for the bottom rail and the window covering, and the lifting mechanism allows the lifting cords to be concealed in the body of the window covering. The cords are stored on spools associated with the lifting mechanism. Spring motors are well-known and generally include a flat ribbon of pre-stressed spring metal coiled to have a natural or relaxed state in which the spring forms a tightly wound coil. Although a variety of lifting mechanisms presently exist, improvements in lifting mechanisms are needed. It would be desirable to provide an inexpensive and compact window covering lifting mechanism and improved locking devices for such lifting mechanisms.